Geeklog comes in a gzip-compressed tarfile (hence .tar.gz). Sometimes, the tarball gets uncompressed during download and you'll end up with a .tar file that's still named .tar.gz. In that case, try leaving out the 'z' from the command line:
Text Formatted Code
tar xf geeklog-1.5.1.tar.gz
The filesize can also be used as an indicator: The compressed tarball is around 4.5 MB in size. If the file you have is much bigger than that, then it got uncompressed.